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Researchers claim to have discovered a security flaw in HP LaserJet printers that permits the installation of malicious firmware that might be capable of disabling safety controls.

In a demo, Columbia University's Professor Salvatore Stolfo and Ang Cui show how it might be possible to instruct a hacked printer to overheat a component used to dry ink, causing paper to heat up and eventually smoke. In the demo a thermal switch caused the printer to shut down before a fire started, but the researchers reckon this too could be disabled, creating a possible mechanism for hackers to use vulnerable printers to start fires.

HP disputes this, stating that thermal switches in its printers are outside the control of firmware updates. "[The thermal breaker] cannot be overcome by a firmware change or this proposed vulnerability," it said.

More unimaginative miscreants could use compromised printers as spying devices, extracting information from print and scanning jobs from attacked devices.

The security shortcoming stems from a failure to mandate digitally signed firmware updates sent to (at least older) printers. So a booby-trapped update could be applied without checks, providing a hacker manages to send it to the device. Exploit scenarios would range from tricking marks into printing maliciously constructed documents to remotely applying updates to internet-accessible printers, the sort of thing even the most basic firewall setups ought to block.

HP told MSNBC, which was the first to report the vulnerability, that its LaserJet printers have required digitally signed firmware updates since 2009. The printer giant said the researchers must have used older models, a point disputed by the Columbia team who say they brought the printer they used in the demo for an office supplies outlet in New York only two months ago. HP is reportedly investigating the issue to determine a list of devices that might be at risk of attack.

Modern printers and scanners are, essentially, computers themselves, so compromising a device within a corporate network might allow hackers to use the equipment as a beach head within a business's defences for attacks on more sensitive systems, such as databases.

It's unclear whether manufacturers other than HP, the market leader, build devices that might also be vulnerable to the same sort of firmware manipulation attack demonstrated by the Columbia team. ®